Techno-economic analysis of hybrid adiabatic compressed-air and biomass gasification energy storage systems for power generation through modelling and simulation

Energy storage has gained an increasing attention as a technology to smoothen out the variations associated with renewable energy power sources and adapt them into a dispatchable product to meet variable demand loads. An energy storage system can be a hybrid or stand alone. There is a rising interest for hybrid energy storage systems cited close to local consumers which is able to exploit the amount of local renewable sources on site, to provide demand side flexibility and also help to decarbonize the heating sector. The thesis is based on modelling and simulation of overall thermodynamic performance and economic analysis of an integrated hybrid energy storage system consisting of adiabatic compressed air energy storage (A-CAES), biomass gasification system with a wood dryer coupled to a syngas-diesel fuelled electric generator for the dual production of electricity and low temperature hot water for domestic use. The first part of the research work involves the modelling of the latent heat (LH) thermal energy storage (TES) for the A-CAES component. Implicit finite difference technique was applied to discretize the energy equations of the heat transfer fluid and phase change material and the resulting equations solved using a developed Matlab computer code. The developed model of the LH TES was validated using experiment measurement from literature and its performance assessed using charging rate, energy efficiency and exergy efficiency. The second part consists of modelling of biomass gasification through a developed Matlab computer code. Kinetic free stoichiometric equilibrium modelling approach was adopted. The developed model showed good agreement with two different experimental measurements. Predictions that can be done with the model include syngas yield, temperature profiles of the pyrolysis, oxidation and reduction zones respectively including syngas yield, carbon conversion efficiency and lower calorific value of the syngas. In the third part, thermodynamic modelling of the overall novel integrated system is developed. It combines the models of different components of the integrated system earlier developed. The system designed for a maximum capacity of 1.3 MW is to utilize the high syngas temperature from the biomass gasifier and the relatively hot dual fuel engine (DFE) exhaust temperature to heat up the compressed air from the A-CAES component during the charging and discharging modes, respectively. Also, the heat contained in the DFE jacket water is recovered to produce low temperature hot water for domestic hot water use. Key output parameters to assess the performance of the hybrid systems are total system efficiency (TSE), round trip efficiency (RTE) of the A-CAES, electrical efficiency, effective electrical efficiency, and exergy efficiency for the system. Furthermore, exergy destruction modelling is done to ascertain and quantify the main sources of exergy destruction in the systems components. Finally, an economic feasibility of the overall system is presented using the electricity and heat demand data of Hull Humber region as a case study. The results of this study reveals that it is technically possible to deploy the proposed system in a distributed generation to generate dispatchable wind power and hot water for domestic use. The total energy and exergy efficiency of the system is about 37.12% and 28.54%, respectively. The electrical and effective electrical efficiency are 29.3 and 32.7 %, respectively. In addition, the round trip efficiency of the A-CAES component of the system is found to be about 88.6% which is higher than that of a standalone A-CAES system, thus demonstrating the advantage of the system to recover more stored wind electricity than in conventional A-CAES system. However, the TSE of the system is less than that of a conventional A-CAES system but comparable to similar hybrid configurations. The exergy destruction of the hybrid system components is highest in the biomass gasifier followed by the DFE and the least exergy destruction occurs in the HAD. Furthermore, economic analysis results show that the system is not profitable for commercial power generation unless a 70% of the total investment cost is waived in the form of subsidy. Expectedly, the cost of electricity (COE) of £0.19 per kWh is more than the range of the mean electricity tariff for a medium user home in the UK including taxes which is £0.15 per kWh. With a subsidy of 70%, the system becomes profitable with a positive NPV value of £137,387.2 and COE of £0.10 per kWh at the baseline real discount rate of 10%. The main contribution of the thesis is that it provides an intergraded realistic tool that can simulate the future performance (thermodynamic and economic) of a hybrid energy storage system, which can aid a potential investor to make informed decision on the profitability and financial outlays for the investmen

Dynamic Analysis of Series-Connected and Mechanically-Coupled Twin Synchronous Motor Drive

Series-connection of the stator windings of electric motors could serve a number of purposes, including load balancing between two synchronous motors. This paper modeled and analyzed a drive system of two separate three-phase synchronous motors whose stator windings are series- connected by a unique stator winding scheme, and whose shafts are mechanically coupled to a common load shaft through a speed reduction gear driven through the pinions of the respective motors. The mathematical model is developed in detail, and the system is simulated using MATLAB/SIMULINK. It is observed that for the case of a balanced load on the respective shafts of the two motors, the dynamic behavior of the two motors are identical. It is further observed that with the particular stator winding arrangement giving rise to six-windings per motor unit, each motor is essentially a three-phase motor and may be operated direct on line (DOL). Keywords: Common load shaft; DOL; series-connected stator windings; synchronous motors, six-winding machin

Modeling and Simulation of Five-Phase Induction Motor Fed With Pulse Width Modulated Five-Phase Multilevel Voltage Source Inverter Topologies

This paper presents modelling and simulation of five-phase induction motor fed with pulse width modulated five-phase multilevel voltage source inverter. The conventional and diode clamped multilevel five-phase inverter configurations are reviewed with pulse width modulation (PWM) techniques. A hybrid three-level inverter topology with less number of components count is proposed for five-phase induction motor drive. The dynamic analysis of five-phase voltage equations in d-q axis of the induction motor are stated and modelled usingMatlab/Simulink/Simscape blocks. The simulation results based on conventional and threelevel five-phase inverters are displayed while the hybrid inverter topology showed some better performance based on the following: : at 0.0127secs maximum torque of 34.54Nm occurred, maximum stator current occurred for 0.18secs with a value of 10A, 9.99% total harmonic distortion was obtained and 15KW power rating was obtained

A Novel Control DC-DC-AC Buck Converter for Single Phase Capacitor-Start-Run Induction Motor Drives

A novel control DC-DC-AC buck converter for single phase capacitor-start-run induction motor drives is presented in this paper. The objective is to minimize harmonic distortion in inverter output voltage supply to a Single Phase Induction Motor (SPIM). Here, the output of a variable duty cycle buck DCDC converter is fed to an H-bridge inverter to generate a very close sinusoidal output voltage. Few power semiconductor switches are utilized to produce inverter output voltage with reduced harmonic distortion comparable with results achieved in multilevel inverters. The SPIM was analysed in the stationary d-q reference frame while the buck converter was operated in the Continuous Conduction Mode (CCM) to ensure that the output voltage vary exactly as the duty cycle. The simulation results show good starting transient characteristics for the SPIM and also stable operation under intermittent loading of 4 N-m. The average inverter output voltage of 157.4 V was achieved with Total Harmonic Distortion (THD) as low as 6.32 %. This configuration is simple, cheap, and has reduced control complexity

Modelling of down-draft gasification of biomass - An integrated pyrolysis, combustion and reduction process

A gasification model is developed and implemented in Matlab to simulate a downdraft gasifier using wood as feedstock. The downdraft gasifier was conceptually divided into three zones: the pyrolysis zone, the combustion/oxidation zone and the reduction zone. A typical tar composition and its mole fraction, as reported in the literature was supplied as an input parameter in the model. The concentration of syngas and profiles of temperature along the reduction zone length were obtained by solving the mass and energy balances across each control volume and taking into account the rate of formation/consumption of the species according to different gasification kinetics. The simulation results from the model agreed closely with the experimental results. The syngas concentration was found to be about 1.1%, 17.3%, 22.8%, 9.0% and 49.8% for CH4, H2, CO, CO2, and N2 respectively and the corresponding LHV, CGE, CCE and yield were 4.7 MJ/N m3, 59.9%, 85.5% and 2.5 N m3/kg-biomass respectively at ER of 3.1 and fuel moisture content of 18.5 wt% Sensitivity analysis was carried out with this validated model for different air-fuel ratios, moisture contents and inlet air temperature. The analysis can be applied to produce specific design data for a downdraft biomass reactor given the fuel composition and operating conditions

Assessment of biomass energy potential for SRC willow woodchips in a pilot scale bubbling fluidized bed gasifier

The current study investigates the short rotation coppice (SRC) gasification in a bubbling fluidized bed gasifier (BFBG) with air as gasifying medium. The thermochemical processes during combustion were studied to get better control over the air gasification and to improve its effectiveness. The combustion process of SRC was studied by different thermo-analytical techniques. The thermogravimetric analysis (TGA), derivative thermogravimetry (DTG), and differential scanning calorimetry (DSC) were performed to examine the thermal degradation and heat flow rates. The product gas composition (CO, CO2, CH4 and H2) produced during gasification was analyzed systematically by using an online gas analyzer and an offline GC analyzer. The influence of different equivalence ratios on product gas composition and temperature profile was investigated during SRC gasification. TG/DTG results showed degradation occur in four stages; drying, devolatilization, char combustion and ash formation. Maximum mass loss ~70% was observed in devolatilization stage and two sharp peaks at 315–500 °C in TG/DSC curves indicate the exothermic reactions. The temperature of gasifier was increased in the range of 650–850 °C along with the height of the reactor with increasing equivalent ratio (ER) from 0.25 to 0.32. The experimental results showed that with an increment in ER from 0.25 to 0.32, the average gas composition of H2, CO, CH4 decreased in the range of 9–6%, 16–12%, 4–3% and CO2 concentration increased from 17 to 19% respectively. The gasifier performance parameters showed a maximum high heating value (HHV) of 4.70 MJ/m3, Low heating value (LHV) of 4.37 MJ/m3 and cold gas efficiency (CGE) of 49.63% at 0.25 ER. The ER displayed direct effect on carbon conversion efficiency (CCE) of 95.76% at 0.32 ER and tar yield reduced from 16.78 to 7.24 g/m3 with increasing ER from 0.25 to 0.32. All parametric results confirmed the reliability of the gasification process and showed a positive impact of ER on CCE and tar yield